Explosive forging of external surfaces

ABSTRACT

IN ORDER TO BLOCK OR FILL EROSION-PRODUCED CHANNELS IN HEAT EXCHANGER TUBE SHEETS, A PLASTIC ROD IS PROVIDED FOR INSERTION INTO A TUBE IN THE EXCHANGER ADJACENT THE EROSION CHANNEL. THE ROD PERIPHERALLY CARRIES AN EXPLOSIVE SO THAT THE LATTER IS PLACED IN CONTACT WITH THE INNER WALL OF THE TUBE WHEN THE ROD IS INSERTED THEREIN. THE ROD IS ORIENTED WITHIN THE TUBE SO THAT THE EXPLOSIVE IS ADJACENT THE CHANNEL. WHEN DETONATED, THE EXPLOSIVE CAUSES THE OUTER WALL OF THE TUBE ADJACENT THE EROSION CHANNEL TO FLOW INTO THE CHANNEL WITHOUT SIGNIFICANT DISTORTION OF THE INNER WALL OF THE TUBE.

Lieberman June 28, 1974 EXPLOSIVE FORGING OF EXTERNAL SURFACES [75]Inventor: Irving Lieberman, Covina, Calif.

[73] Assignee: Whittaker Corporation, Los

Angeles, Calif.

[22] Filed: July 13, 1973 [21] Appl. No: 379,061

521 U.S.Cl ..29/401,29/157.4,29/421 511 1nt.Cl B23p 17/00 [58]FieldofSearch 29/421 R, 421E, 401 R,

[56] References Cited UNITED STATES PATENTS 3,503,110 3/1970 Berry etal. 29/421 E 3,717,925 2/1973 Hardwick 29/157.4 X 3,781,966 1/1974Lieberman 29/401 Primary ExaminerCharles W. Lanham Assistant Examiner-V.A. DiPalma Attorney, Agent, or FirmDonald E. Nist; Jay H. QuartzABSTRACT In order to block or fill erosion-produced channels in heatexchanger tube sheets, a plastic rod is provided for insertion into atube in the exchanger adjacent the erosion channel. The rod peripherallycarries an explosive so that the latter is placed in contact with theinner wall of the tube when the rod is inserted therein. The rod isoriented within the tube so that the explosive is adjacent the channel.When detonated, the explosive causes the outer wall of the tube adjacentthe erosion channel to flow into the channel without significantdistortion of the inner wall of the tube.

5 Claims, 5 Drawing Figures This invention relates to explosive forgingand, more specifically, it relates to the forging of heat exchangertubes by explosive means into erosion channels in heat exchanger tubesheets.

When tube ends are expanded in tube sheets in heat exchangers, a fitmismatch can occur between the tube sheet and tube. This can result inthe formation of very small cavities or crevices between the tube andtube sheet. When a fluid flows into such cavities, they can increase insize to a point where they may extend completely through the tube sheetwith the result that fluid can leak out of the heat exchanger throughthe erosion channels thus formed.

Heretofore, further expansion of the tubes within the tube sheets byexplosive forming methods such as that which is described in U.S. Pat.No. 3,4l l,l98, issued Nov. l9, I968 (hereinafter referred to as saidUS. Pat), after such erosion channels have been formed, has been foundto be inadequate due to the small width and depth of the channels(usually on the order of 0.020 in. 0.50 in.). That is, such explosiveforming methods are unable to force tube metal into these small channelsbecause these methods produce a relatively uniform expansion of the tubeand because the tube thickness imposes restrictions on localizedexpansion of the tube metal. Furthermore, the disassembly of a heatexchanger to remove the affected tubes in order to fill the channels bywelding and grinding is extremely expensive. Therefore, there ispresently no satisfactory way to solve the problems created by theformation of erosion channels in heat exchangers.

SUMMARY OF THE INVENTION This invention comprises the placement ofexplosives in contact with the inner wall of a tube adjacent an erosionchannel so that when an explosive is detonated, that portion of theouter wall of the tube which is adjacent to the erosion channel isforged or expanded into the erosion channel.

A primary advantage of this technique is that it provides a substantialcost saving over prior art techniques since it does not require that theheat exchanger be inoperable for a long time. Additionally, the erosionchannels are suitably blocked without significant distortion of theinner surface of the affected tube. This means that flow conditionswithin the tube are essentially uneffected.

DESCRIPTION OF THE DRAWINGS FIG. 1 is a perspective view of a portion ofa tube sheet showing a typical tube extending therethrough together withan erosion channel in the tube sheet alongside the tube.

FIG. 2 is an end-elevational view of the tube and tube sheet of FIG. 1.

FIG. 3 is a perspective view of an insert containing a peripherallylocated explosive charge.

FIG. 4 is an end-elevational view of the tube and tube sheet of FIG. Iwith the insert of FIG. 3 positioned therein.

FIG. 5 is a perspective view of the tube of FIG. 1 after the explosivecharge contained in the insert has been detonated.

DESCRIPTION OF THE PREFERRED EMBODIMENT In FIG. 1, the numeral 10designates a tube sheet through which a plurality of tubes such as thatdesignated by the numeral 12 normally extend. Each tube 12 is positionedwithin an elongated hole 14 within the tube sheet 10 and is usuallyexpanded therein against the walls of the tube sheet which define thehole 14 by mechanical means or by explosive means such as is describedin said U.S. patent. Each tube 12 is characterized by a bore 18extending therethrough and defined by an inner surface or wall 20.

Erosion channels such as the one indicated by numeral 16 may be formedin the tube sheet 10 adjacent to the outer surface 21 of the tube 12.Such channels 16 may extend along the tube 12 in parallel relation withthe tube axis or they may be non-linear as shown in FIG. 1 and FIG. 2.

In FIG. 3, there is shown an insert 22 having an outside diameter ofsubstantially the same size and shape as the inside diameter of the tube12. The length of the insert 22 will depend upon the shape and length ofeach erosion channel 16. The insert 22 is provided with a peripheralchannel 24 which extends longitudinally of the insert. This channel 24may be wholly or partially filled with an explosive 26 which ishereinafter referred to as a forging explosive. Additionally, thechannel 24 may be open as shown in FIG. 3 or it may have a thin coveringof the insert material to aid in retaining the explosive in the insert22. An explosive 28 (which will be referred to hereinafter as a formingexplosive) may be carried axially within the insert 22 for expanding atube into a tube sheet as described in said U.S. patent.

The insert 22 may be made from any material which will not spall andscore the inner surface 20 of the tube 12 when the forging explosive 26is detonated. Preferably, the insert 22 is made from a castable orextrudable material. Useful materials from which the insert 22 may bemade include plastics, rubber and wood.

The explosive which is selected as the forging explosive 26 must be onewhich will produce a shock wave which is strong enough to cause at leastlocalized extrusion of the tube metal at its outer surface, but which isnot so strong that it causes spalling of metal from a tube. The strengthof a shock wave which is otherwise sufficiently strong to produce thedesired extrusion may, of course, be rendered ineffective for thispurpose if it has to travel through materials which cannot transmit theshock or which can transmit it but in reduced strength. Therefore,location of the forging explosive 26 relative to the erosion channel 16is critical.

The forging explosive 26 must be in substantial contact with the innersurface 20 of the tube 12. Substantial contact is effected by (1) actualcontact of the forging explosive 26 with the tube inner surface 20, (2)by positioning the forging explosive 26 in the insert 22 so that theshock passes through only a very thin overlying layer of insertmaterial, or (3) by employing ex plosive which is provided with asurround or wrapping such as in the case of an explosive sold asPrimacord if the tube wall thickness is quite thin, i.e., on the orderof 0.020 in. or less. If, in the case of (3), the tube wall thickness ison the order of 0.050 in. 0.060 in. or greater, a contact explosiveshould be employed, otherwise the shock wave will not be able to produceextrusion of the tube outer surface region.

The explosive employed as the forging explosive 26 may be any well-knownexplosive which produces the aforementioned extrusion. For example, anyof the following explosives may be employed: strips of Dupont deta sheet(containing PETN); pressed composition C-4 (containing RDX); castexplosives such as composition B (60 percent RDX, 40 percent TNT); andpressed desensitized RDX.

The explosive employed as the forming explosive 28 may be the same as,or different from, the explosive employed as the forging explosive 26.Thus, any of the above explosives or other explosives such as Primacordmay be employed as the forming explosive 28.

In order to fill the erosion channel 16, the insert 22 containing theforging explosive 26 is inserted into the tube 12 to a desired depth (HQ4). The insert 22 is rotated until the forging explosive 26 is placedopposite the erosion channel 16 or until the forging explosive 26 ispositioned so that it intersects the erosion channel preferably at aplurality of points. Thereafter, the forging explosive 26 is detonatedin a conventional manner. As previously noted, the insert 22 may alsocontain forming explosive 28 and, if it does, the forming and forgingexplosives may be detonated substantially simultaneously although theforging explosive 26 may be detonated slightly later than the formingexplosive 28.

The effects of forging by the herein-described method are shown in FIG.5. As that figure shows, the outer surface 21 of the tube 12 has beenextruded to form a protruding rib 30 having a cross-sectional shapesubstantially the same as that of the erosion channel 16. It will alsobe noted in FIG. that the inner surface of the tube has not beensignificantly altered.

This invention has been described by showing the use of a straightexplosive-containing channel 24. However, this is not necessary.Instead, the insert channel 24 can be made to follow the contour of theerosion channel 16 to plug it for a desired continuous distance ratherthan to plug it at spaced locations as when using a linear insertchannel 16. This is accomplished when the orientation and location ofthe erosion channel is known and clearly defined.

I claim:

1. Amethod of blocking an erosion channel formed in a metal memberadjacent the outer surface of a tube extending through said member, saidmethod comprismg:

providing an insert which has an outside diameter substantially equal tothe inside diameter of a tube and which defines a peripheral channel;inserting a forging explosive into said channel so that said explosiveis in substantial contact with the inner surface of said tube, saidexplosive having sufficient strength to cause extrusion of the materialforming said tube adjacent said explosive;

slidably inserting said insert into said tube;

orienting said insert in said tube with respect to said erosion channelso that at least some of said tube material adjacent said explosive willbe extruded into said erosion channel; and

detonating said explosive.

2. The method of claim 1 wherein said channel in said insert is spacedfrom and parallel to a longitudinal axis of said insert.

3. The method of claim 1 wherein said channel in said insert describesan arcuate path.

4. The method of claim 1 wherein said insert contains a formingexplosive extending along a longitudinal axis thereof and wherein saidmethod further includes the step of:

substantially simultaneously detonating said forming explosive and saidforging explosive to cause expansion of said tube into contact with saidmember and extrusion of some of said tube material into said erosionchannel.

5. The method of claim 4 wherein said forming explosive is the same assaid forging explosive.

